1. Technical Field
The present invention relates generally to broadcasting and communications technology, and more particularly to technology for receiving signals based on Faster-Than-Nyquist (FTN).
2. Description of the Related Art
General communications systems use a Nyquist pulse-shaping method in order to transmit signals without interference between symbols. The Nyquist pulse-shaping method is a pulse-shaping method that is capable of achieving the maximum transmission rate in a given bandwidth without interference between symbols. However, in recent communication systems, requirements for higher spectral efficiency are increasing, but the Nyquist pulse-shaping method has a limitation as to transmission efficiency. Accordingly, as a method for improving this, the Faster-Than-Nyquist (FTN) method has been introduced.
In the FTN method, a pulse shape, given depending on frequency bandwidth, is kept, but the time interval between shaping of a pulse and shaping of the next pulse is decreased. That is, the gap between symbols is narrowed, whereby a signal, the pulses of which overlap each other, is transmitted. Accordingly, the FTN method necessarily causes Inter-Symbol Interference (ISI), but may have a higher signal transfer rate than the Nyquist pulse-shaping method for the same bandwidth.
As described above, the FTN method may improve transmission speed, but ISI, which is not caused in the Nyquist method, is included in a signal during the process of generating the signal and is transmitted when the signal is transmitted. Therefore, a receiver needs to eliminate ISI (hereinafter, referred to as “FTN interference”) caused by FTN in order to reconstruct data without errors.
Because FTN interference is intentionally generated in the process of generating a signal to be transmitted, the pattern is accurately known, and thus FTN interference may be eliminated from the received signal. That is, a receiver generates a reference signal in which original data includes intentional interference caused by FTN, the received signal is compared with the reference signal, and thereby data from which the interference is eliminated is reconstructed. Also, if a pulse-shaping filter has a large enough number of taps to generate a bandlimited signal, FTN interference generated through such long filter taps causes interference between neighboring symbols in a wider range. Here, if a receiver cannot sufficiently eliminate the interference, it is difficult to improve reception performance, but if the range of the interference between neighboring symbols to be processed is wider, reception performance is improved, but complexity is increased.
Meanwhile, Korean Patent Application Publication No. 10-2015-0097048, titled “Signal-receiving apparatus based on Faster-Than-Nyquist and signal-decoding method thereof relates to an apparatus for receiving FTN-based signals and a method for decoding FTN-based signals. This patent discloses a signal-receiving apparatus based on FTN, which includes an equalizer for calculating, when a signal sampled with Faster-Than-Nyquist (FTN) is received on a communication channel, a posterior probability of information bits for the received signal through the BCJR algorithm and for calculating a Log Likelihood Ratio (LLR) using the calculated posterior probability; a deinterleaver for deinterleaving bit data output from the equalizer; a decoder for compensating for signal interference of the data bits deinterleaved by the deinterleaver using the LLR, thereby decoding the data; and an interleaver for interleaving the data output from the decoder and providing the interleaved data to the equalizer.
However, Korean Patent Application Publication No. 10-2015-0097048 does not mention a problem related to FTN interference occurring at a receiver of FTN-based signals.